Hi , further to my last post I have attached the question and answer .
I don't understand where the limit of d came from and the value of k to evaluate the
last 2 lines in the answer .
I recognize this paper! The "d" in the mark scheme here just means that a candidate would be awarded the A1 accuracy mark regardless of whether they had calculated that limit correctly. However, you wouldn't achieve the B1 final base mark for an incorrect limit. The same applies to the value of k.